You still need UVs to paint with any painting tool that isn’t based on PTex or Mesh Colors. Painting directly on the model just means that the quality of those UVs doesn’t matter nearly as much as it used to. Smart UVs and other auto unwrapping algorithms could theoretically work just fine for you for non-hero assets, and some 3D painters could even do this themselves if they detect a model with no UVs (and I believe that some even have this option, maybe even Armor Paint), but UVs themselves are still very integral to CG and texturing. UDIM has more or less superseded regular UVs as the unwrapping method of choice, and have very much won out over PTex in the majority of the production world, but they’re still just regular old UVs at their core.

Smart UVs and other auto unwrapping algorithms could theoretically work just fine for you for non-hero assets, and some 3D painters could even do this themselves if they detect a model with no UVs (and I believe that some even have this option, maybe even Armor Paint),

Ok, I had to DuckDuckGo a ton of what you said.
What does this statement mean? What is a “non hero asset”?

Does Blender have Ptex and UDIM? (I’m still dipping my toe in the water here…)

In the industry a hero asset is a character, set piece, or prop that is going to be front and center as the focus of a shot. This generally means that it’s going to have a lot more attention paid to its quality, including the quality of its UVs. Most other assets are just made “good enough” for the shot in the sake of time and budget.

No it definitely still is. Background characters, props, and places the player are likely to go get less attention to detail. Stretched textured due to automatically generated UVs are very common in games once you go off of the beaten path, as are lower res textures for out-of-the-way decals and props, and less fluid animations for filler characters, especially in open world games.